Process of producing dense and firmly-adhering tin deposits



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na e srarasenrsnr oeencei MAX SCHLGTTER, OFBEBLTN, GERMANY.

PROCESS OF PRODUCING DENSE AND FIRMLY-ADHERING TIN DEPOSITS.

ea ers.

T 0 albwhom it may concern:

Be it known that I, MAX SoHLorrER, a citizen of the German Republic, residing at No. 87 Bayrentherstrasse, in the. city of Berlin and State of Prussia, have invented electrolytic tin plating processes in spite of the fact that the use of alkaline baths is accompanied the disadvantages that the electrolyte is subject to variation of composition that sponge formation is produced, and a low utilization of on rent obtained. Disregarding the proposal a ready made by others to use an electrolyte containing sodium pyrophosphate, acid tin baths per se have not been known after all.- A bath containing tartaric acid has also been proposed but this proposal was of no practical I value although acid tin baths ofl'erspecia] advantages owing to their high electrochemical equivalents. The reason why acid baths have not been applied is to be traced to the fact that in deposits produced by means of an acid electrolyte show a special crystalline form and do not cover the cathode uniformly butenclose the latter in a lacelike fashion. This drawback appears accentuated when iron is being sought to be tin plated electrolytically. The electrolytically precipitated deposit from an acid solvent has so little adhering power that it is removed completely under the polishing treatment.

owever, even if no account is taken of the fact that tin deposits produced frgm acid solutions are of low adhering power, such depositsare of no use really in electroplats ing in consequence of their tendency to pro- 'duce crystalline growth;

, Now, I have discovered that, dense tin deposits showing no tendency to crystalline growth can be produced out of ordinary tin salt solutions free of alkalies and ammonium when previously small quantities of gelatine or an other colloid are added to the strongly acid electrolyte. It is well known Specification of Letters Patent. Patgnfi edl dug, 22, 1922 Application filed January 21, 1920. Serial No. 353,113.

to use colloids in metallic. baths but the combination of colloids with acid .tin salt solutions free of alkalies is decidedly new since hitherto it has been usual to apply ammonium chloride in order to maintain the stannous chloride in solution provided that the operation was not intended to produce an alkaline bath. 7

It is not necessary to use strongly concentrated tin salt solutions as has been proposed by others, since already a solution containing 120 grams of stannous (sulphate, 2 grams of gelatine, and 100 cubic centimeters of water has lost the tendency to produce crystalline tin precipitations. A Solutions of the above specified kind are well adapted to produce dense and vfirinly adhering tin deposits upon copper, brass, and the like metals. The structure of the. tin. undergoes an'alteration to such an extent that the new structure may be compared with that of electrolytic iron; which is well known to have the least crystalline structure of all electrolytically separated metals when produced in thick layers.

Despite this property, a bath of this com position is not well adapted for the purpose of tin plating iron galvanos. The tin does-not adhere firmly enough to the basic metal and while the tin deposits upon copper have a good covering power the same deposit when precipitated upon iron is composed of small crystalline structure. Al-

though no crystalline. growth is produced phenomenon is a drawback in actual p ac tice. Now, have discovered that this dr wback fcan be overcome by adding to the colloidal tin bath substances of capillary ac tion, that isto say, substances which, when added to the electrolyte, cause the growth of the crystals in the direction ofone or more of their axes to be lessened or suppressed, such, for instance, as phenol, phloroglucin', and the like. obtain useful deposits upon iron from acid solutions by means of a bath composed for instance of 150 grams of stannous chlorid,-

2 grams of gelatine, 5 grams of phenol, 1000 cubic centimetres of water, and 5 grams of hydrochloric acid.

What I claim as my invention and desire I am able to a to secure by Letters Patent of the United States, is:-- .4

1. A process of producing dense and firmly adhering tin deposits, consisting in adding a substance of capillary activity to a tin salt solution, and subjecting the same to the action of an electric current.

. firmly adhering tin deposits, consisting in adding a colloidal substance and a substance of capillary activity to a tin salt solution free of ammonium, and subjecting the same to the action of an electric current. 1

5. A process of producing dense and firmly adhering tin deposits, consisting in adding a colloidal substance and a substance of capillary activity to a tin salt, solution free of alkali and ammonium, and subjecting the same tothe action ofan electric current.

6. A process of producing dense and firmly adhering tin deposits, .consisting in adding to a tin salt solution gelatine and emma phenol and hydrochloric acid, and subjecting the thus produced electrolyte to the action of an electric current.

8. A process for producing dense. and firmly adhering tin deposits, consisting in adding a colloidal substance and a substance of capillary activity to an acid tin salt solutionfree of alkali, and subjecting the same to the actionof an electric current.

9. A process for producing dense and firmly adhering tin deposits, consisting in adding a colloidal substance and a substance of capillary activity to an acid tin salt solution free of ammonium, and subjecting the same to the action of an electric current.

10. A process of producing dense and firmly adhering tin deposits, consisting-in adding a colloidal substance and a substance of capillary activity to an acid tin'salt solution free of alkali and ammoniumand subjecting the same to the action, of an electric current.

lntestimony whereof I have signed my name to this specification in the presence of two subscribing witnesses. n

. MAX SCHLOTTER. Witnesses:

EMIL HOFFMANN, PAUL BRAUN. 

